PURPOSE: To make the effective length of an excavating shaft longer, and enhance a working efficiency by forming the excavating shaft slidably supported on a leader out of mutiple hollow pipes, letting power for an supported excavating means and a lifting means be supplied from a single prime mover set at the lower section.

CONSTITUTION: The excavating shaft 26 which is slidably supported by the leader 22 of an excavator 21 in a place such as the inside of a tunnel where a working height is limited, is formed out of multiple hollow pipes, and concurrently an excavating shaft drive means 23 and an excavating shaft lifting means 24 are disposed at the lower section and the upper section respectively via a speed change transmitting mechanism. Besides, a prime mover 25 is set in the lower drive means 23 so as to allow an excavating blade and the like to be rotated, and also to allow the lifting means 24 to be driven via the excavating shaft 26. In addition, the center of gravity of the leader 22 is lowered to prevent the leader from falling down, and concurrently the drive means 23 and 24 are made thin in thickness to lengthen the effective length of the excavating shaft 26 as much as possible, so that the number of shaft replacement is thereby reduced. Besides, an injection path for coolant and cement milk and the like is provided for the inside of the excavating shaft 26. By this constitution, works can thereby be efficiently carried out.